The present invention relates to refiners for defibrating high consistency lignocellulosic chips and the like at superatmospheric heat and pressure, and more particularly, to the feeding of chips to the rotating disc or discs in such refiners.
The problem of feeding chips under superatmospheric heat and pressure, to the rotating discs of a disc refiner, have been addressed in a variety of ways including the use of a helical ribbon feeder in a cylindrical conveyor housing, mounted coaxially with the rotating disc. An example is shown in U.S. Pat. No. 5,076,892 (Fisher et al), wherein the ribbon feeder assembly not only conveys the chip material toward the refiner disc, but also permits the coaxial extraction of back flowing steam that has been generated at the disc by the refining process. In some instances, the ribbon feeder is driven independently of the main drive shaft of the disc, and in other instances, it is driven co-rotatably with such drive shaft.
As the chips are conveyed axially toward the inlet region of the rotating disc, the chips experience a very high centrifugal force, which urges the chips radially against the conveyor housing. The axial component of force, which is of primary importance for conveying the material toward the disc, is of significantly lesser magnitude. Although the helical ribbon shape itself provides some axial component for conveying the chips, a convenient way of providing additional axial force on the chips is desired, to overcome increased backflow steam forces that are generated as designers produce higher power refiners.